If your child is diagnosed with cancer, it may feel as though you went to bed one night and woke up in an alternate universe. Suddenly there are all these new words — oncology, chemotherapy, radiation — not to mention a slew of new fears and emotions.

Now the doctor is saying your child's immune system isn't strong enough for him or her to go to school or even visit family.

If that's the case, chances are it's because your child has developed a condition called neutropenia. Neutropenia is when the body has very low levels of certain white blood cells (called neutrophils), the body's main defense against infection.

Cancer and its treatment also may cause other problems with the immune system, making it important to avoid crowds of people who could expose your child to viruses.

A Weakened Immune System

When a germ enters the body, a healthy immune system springs into action, sending an army of neutrophils to the area to attack. The next time those same germs enter the body, the immune system will "remember" them and try to head them off before they can cause any serious trouble.

Someone with cancer, though, often has fewer neutrophils patrolling the body. In some cases, that's because the cancer itself damages the bone marrow, the spongy material inside the bones where all new blood cells — including neutrophils — are made. (This is especially common with cancers like leukemia and lymphoma.)

Other times it may be the cancer treatments themselves that are doing the damage. Both chemotherapy (powerful cancer-fighting drugs) and radiation (high-energy X-rays) work by killing the fastest-growing cells in the body — both bad and good. That means that while cancer cells are destroyed, so too are healthy blood cells, like neutrophils.

Risk of Illness

With fewer neutrophils, a person is more prone to infection. Even things the body would normally be able to fight off without much trouble, like skin infections or ear infections, become much more serious and long-lasting when someone is in a "neutropenic state."

That's why it's important to call the doctor right away if your child has a fever, shaking or chills, or any mouth or skin sores, which can be signs of infection.

Fortunately, doctors can use a blood test called an absolute neutrophil count (ANC) to judge how cautious someone needs to be about avoiding germs:

When the neutrophil count is below 1,000 cells per microliter of blood, the risk of infection increases somewhat.

When it falls below 500 cells per microliter, the risk increases quite a bit more.

If it stays below 100 for many days, the risk of serious infection becomes very high.

Sometimes, medicines called growth factors can be given to encourage the body to produce more neutrophils. But often it's safest for a child to remain home for a length of time determined by the doctor. Places like schools, locker rooms, malls, and even churches — where people are close together and germs spread easily — are just too risky. To a child's weakened immune system, it would feel like standing at the edge of a forest fire with only a water gun for defense.

Making the Best of It

Being stuck at home can be tough on anyone. When things feel out of control, most people — and especially kids — count on the routines of daily life to help maintain some sense of normalcy. It's only natural that losing that, even temporarily, can leave your child feeling angry, frustrated, left out, depressed, punished, and even jealous of siblings and friends.

So what can you do to help your child make the best of the time at home?

Plenty — though it may depend on how your child feels. Some days the cancer treatments will wipe your child out, and all he or she will want to do is sleep. Other days your child will have more energy.

Follow your child's lead, and when he or she seems up for it, here are some ideas for beating the boredom:

Help Your Child Stay Connected

Even if you cracked down on screen time before your child got sick, now's a good time to consider easing up. Allowing access to the Internet, texting, online messaging, photo sharing, Skype, and online games with friends is more than just a perk — it's a valuable way for your child to stay within his or her social network.

Ask the doctor or nurse if a friend can come over. In some cases, if the doctor says it's OK, your child might be able to have a friend over for a brief visit or a movie night. If so, a little prep work on both sides can make the evening go smoothly.

First, make sure the friend knows that your child's cancer, and related neutropenia, isn't contagious — otherwise he or she may be reluctant to come. More important for your child's safety, reschedule get-togethers if there's any question about whether the visitor is sick, even if it's just a cold. And finally, always have everyone who comes in contact with your child wash their hands.

Even though it may hurt to talk about this, let your child know that some friends may deal with his or her illness better than others. Remind your child to try not to take it personally if some friends don't know what to say, or if they talk about things that your child missed out on. The good news is that there will usually be a few true friends who will know how to treat your child like the same person he or she has always been.

Get Creative

What are some things your child never gets a chance to do? Maybe your daughter is an athlete who's always wondered if she has an artistic side; or your son is a computer whiz who's always enjoyed creative writing.

Now's the time to explore those other sides of your child's personality. Painting, drawing, building models, designing clothes or jewelry, learning an instrument, or making a scrapbook or collage of favorite photos are all great ways to get those creative juices flowing. Writing poetry or keeping journals or a blog can help your child deal with difficult emotions — and rereading them when your child feels better will be a reminder of how far he or she has come.

Approve a Room Makeover

With a little help from you, your child's bedroom can become the coolest and comfiest space ever. Maybe you can turn a corner into a lounge, or the bed into a funky sofa with fluffy pillows or a reading pillow with arms. Choose colors that make your child feel good and be sure to keep favorite music, books, and photos nearby to really make it special.

Get Outside

Even when public places are off limits, fresh air usually isn't. So encourage your child to sit on the porch or in the yard and read, talk on the phone, or listen to music.

Help Your Child Feel Empowered

One of the best ways for anyone to feel stronger is to do something good — maybe your child can coordinate a fundraiser for a favorite charity, whether it has to do with cancer or another special cause, like animals or the environment. Maybe he or she could start a blog about dealing with cancer that can help other kids in the same position.

Or maybe your child can make a list of things to look forward to when this experience is over. Getting your child to think beyond the here and now can make the time go faster and help everyone stay positive.

Talk It Out

Feelings and worries can become overwhelming when they're held in, so find a way to help your child let them out. A good place to start is with your hospital's social worker, who can put your family in touch with others who've been where you are now.

Or check out some of the many cancer support websites, most with chat areas or message boards, that make it easy to share what your family is going through with others who understand.

Try to Keep Up With Schoolwork

And last but not least, encourage your child to stay on top of schoolwork as much as possible. Keep in touch with teachers to find ways to stay involved in classroom life and modify assignments, when necessary.

Staying home may be hard on kids at first, especially if a child was always on the go. The good news for many kids with cancer is that having to stay home is only a temporary setback. Once the immune system recovers, your child should be able to get back in the swing of things.

In the meantime, keep your child's spirits up, look toward the future, and have confidence that, even though things seem difficult now, your child will get through it with help from loved ones.